Most of remaining unemulated Soviet PC clones are not very interesting, but Istra-4816 is truly weird. It's not clear if it was designed as a PC clone from the start, or retrofitted later, but the finished product definitely runs DOS (and Prince of Persia).
It has three CPUs (two 8080 and one 8086), one 8080 does I/O emulation for the other two, another is described a 'supervisor' and may run its own OS (likely CP/M) concurrently with whatever is running on 8086. All three have shared access to RAM, but only IO cpu has access to ROM. Video hardware uses two 8275s and apparenty can mix text and graphics modes within scan line.
All in all, this is so weird that even with schematics (which are available) and ROMs (not yet) I'm not inclined to work on it